More than 300,000 gastrointestinal resection and anastomosis per year are performed in the U.S. alone. Dehiscence or leakage from anastomotic sites following surgery occurs in 5-15% of patients and is associated with significant post-operative morbidity and mortality. Prior preclinical investigations have shown the importance of adequate tissue oxygenation at the anastomosis in preventing post-operative leakage and complications. Surgeons traditionally assess tissue viability and blood supply by simple visual inspection only. A method to assess anastomotic tissue viability intraoperatively would help perform corrective measures and improve surgical outcomes. We hypothesize that real-time monitoring of tissue oxygenation by wireless pulse oximetry (WiPOX) device provides a reliable, objective measure of tissue perfusion, and can detect tissue ischemia earlier than visual inspection, thereby allowing corrective actions to reduce post-operative morbidity and mortality. Our engineering (CCNY) and surgical (MSKCC) teams collaborated to develop and validate an innovative WiPOX device - this hand-held device and miniature probe provides operating surgeons with real-time, accurate, and convenient monitoring of the tissue oxygenation. This will not only enable the surgeon to monitor vascular compromise in real time in order to rectify any conduit twisting, but will also allow the surgeon to confidently select the site of maximal oxygenation for the anastomosis. This proposal will include pivotal device development and validation steps in three clinical applications (Aims): 1) Using a WiPOX model already validated in pilot clinical trials, we will conduct a prospective clinical trial of patients undergoing esophagogastrectomy, testing whether WiPOX can (a) predict anastomotic leaks resulting from tissue oxygenation (Ti02) compromise, and (b) optimize peri-anastomotic Ti02, thereby decrease post-operative anastomotic leakage. 2) To develop and test a new WiPOX model to detect early flap ischemia in patients undergoing microvascular free tissue transfer for breast reconstruction and conduct a pilot clinical trial. 3) Develop a new platform based on a multi-sensor array embedded in mesh to envelope a liver or heart and test the device in large animals for detecting real-time intraoperative blood flow compromise during liver resections and heart bypass surgery.